Okay, kinda funny example. But it doesn't really matter. The antagonist is the agency or person who makes things difficult for the protagonist. If the protagonist (the main character) is a whaler, bent on killing whales, Greenpeace would be the antagonist. Who is the story about (the main character?) The whaler guy. Who is likely to evolve during the story? The whaler guy. The whaler guy is the protagonist. Who opposes the whaler guy? Greenpeace. Therefore, Greenpeace is the antagonist. If the main character was some Greenpeace activist, who will grow and change during the story, then that person would be the protagonist. If the whaler guy opposes them, then the whaler guy would be the antagonist. It's about the position each of them holds in the story, not about their character's goodness or badness.
Throughout my story, the MC older brother who he admires and looks up to, but becomes the antagonist or the bad guy in the end. His older brother is far opposite of him, a charming asshole, womanizer, smooth talker, bully, peers fear and respect him, while the MC the younger brother is the opposite. It isn't they're assholes directly or even come across as one but they have a charm to them, even looks, charisma to manipulate others, both genders to a certain extent. Think of "Fuckbois", girls always talk about how they hate or complain about them because they always get approached by them with their stupid pick up lines. If a fuckboi gets rejected, they don't care, he goes to the next one. Nice guys are boring as hell, Harry Potter, I hated because he was just dull, boring, nice guy character.
